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<H2>lexicographical_compare()</H2>
<P><B>Module:</B>&nbsp;&nbsp;Standard C++ Library&nbsp;&nbsp;&nbsp;<B>Library:</B>&nbsp;&nbsp;<A HREF="2-9.html">Algorithms</A></P>

<PRE><HR><B><I>Function</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Complexity</A></LI>
<LI><A HREF="#sec6">Example</A></LI>
<LI><A HREF="#sec7">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
No Entries
<A NAME="sec2"><H3>Summary</H3></A>
<P>Algorithm that returns <SAMP>true</SAMP> if one sequence compares lexicographically less than another, <SAMP>false</SAMP> otherwise</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;algorithm&gt;

namespace std {
  template &lt;class InputIterator1, class InputIterator2&gt;
  bool
  lexicographical_compare(InputIterator1 start1,
                          InputIterator1 finish1,
                          InputIterator2 start2,
                          InputIterator2 finish2);

  template &lt;class InputIterator1, class InputIterator2, 
            class Compare&gt;
   bool
   lexicographical_compare(InputIterator1 start1,
                           InputIterator1 finish1,
                           InputIterator2 start2,
                           InputIterator2 finish2, 
                           Compare comp);
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>The <SAMP>lexicographical_compare()</SAMP> functions compare each element in the range <SAMP>[start1, finish1)</SAMP> to the corresponding element in the range <SAMP>[start2, finish2)</SAMP> using iterators <SAMP>i</SAMP> and <SAMP>j</SAMP>. </P>
<P>The first version of the algorithm uses <SAMP>operator&lt;()</SAMP> as the default comparison operator. It immediately returns <SAMP>true</SAMP> if it encounters any pair in which <SAMP>*i</SAMP> is less than <SAMP>*j</SAMP>, and immediately returns <SAMP>false</SAMP> if <SAMP>*j</SAMP> is less than <SAMP>*i</SAMP>. If the algorithm reaches the end of the first sequence before reaching the end of the second sequence, it also returns <SAMP>true</SAMP>. </P>
<P>The second version of the function takes an argument <SAMP>comp</SAMP> that defines a comparison function that is used in place of the default <SAMP>operator&lt;()</SAMP>.</P>
<P>The <SAMP>lexicographical_compare()</SAMP> functions can be used with all the data types included in the standard library.</P>
<A NAME="sec5"><H3>Complexity</H3></A>
<P><SAMP>lexicographical_compare()</SAMP> performs at most <SAMP>min((finish1 - start1), (finish2  -  start2))</SAMP> applications of the comparison function.</P>
<A NAME="sec6"><H3>Example</H3></A>

<UL><PRE>//
//  lex_comp.cpp
//

#include &lt;algorithm&gt;
#include &lt;functional&gt;
#include &lt;iostream&gt;
#include &lt;vector&gt;

int main()
{
    typedef std::vector&lt;int, std::allocator&lt;int&gt; &gt; Vector;

    const Vector::value_type d1[] = { 1, 3, 5, 32, 64 };     
    const Vector::value_type d2[] = { 1, 3, 2, 43, 56 };

    // Create vectors.
    Vector v1 (d1 + 0, d1 + sizeof d1 / sizeof *d1);
    Vector v2 (d2 + 0, d2 + sizeof d1 / sizeof *d2);

    // Is v1 less than v2 (I think not).
    bool b1 = std::lexicographical_compare (v1.begin (), 
                      v1.end (), v2.begin (), v2.end ());
 
    // Is v2 less than v1 (yup, sure is).
    bool b2 = std::lexicographical_compare(v2.begin (), 
                      v2.end (), v1.begin (), v1.end (),
                      std::less&lt;int&gt;());

    std::cout &lt;&lt; std::boolalpha &lt;&lt; b1
              &lt;&lt; " " &lt;&lt; b2 &lt;&lt; std::endl;

    return 0;
}


Program Output:
</PRE></UL>
<UL><PRE>false true

</PRE></UL>
<A NAME="sec7"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.3.8</I></P>

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